The regulation of herpes simplex virus IE (immediate early) gene expression is mediated by the assembly of a multiprotein transcriptional enhancer complexes containing both cellular and viral proteins. This assembly provides a biochemically accessible model system for the analysis of DNA-protein and protein-protein interactions involved in the regulation of RNAPII directed transcription. Several of the proteins involved have been well characterized. However, the functions of the critical coordinator of the enhancer assembly (C1 factor) have not been well defined. Therefore, the primary objectives have been to determine the role of this protein in both viral and cellular processes. Analysis of domains and interactions of the C1 factor have determined that the protein interacts with other cellular and viral transcription factors in the regulation of viral and cellular genes. These studies identified a number of mammalian genes that include additional cellular trancription factors which are also involved in the expression of the HSV IE genes. - Herpes, transcription, gene regulation, coactivator